paymod: Implement keysend sending support as a native RPC command

This makes use of the payment modifier structure to just add the preimage to
the TLV payload for the last hop.

Changelog-Added: JSON-RPC: The `keysend` command allows sending to a node without requiring an invoice first.

tests/plugins/keysend.py

@@ -1,118 +0,0 @@
-#!/usr/bin/env python3
-"""Temporary keysend plugin until we implement it in C
-
-This plugin is just used to test the ability to receive keysend payments until
-we implement it in `plugins/keysend.c`. Most of this code is borrowed from the
-noise plugin.
-
-"""
-
-from pyln.client import Plugin, RpcError
-from pyln.proto.onion import TlvPayload, Tu32Field, Tu64Field
-from binascii import hexlify
-import os
-import hashlib
-import struct
-
-
-plugin = Plugin()
-TLV_KEYSEND_PREIMAGE = 5482373484
-
-
-def serialize_payload(n, blockheight):
-    """Serialize a legacy payload.
-    """
-    block, tx, out = n['channel'].split('x')
-    payload = hexlify(struct.pack(
-        "!cQQL", b'\x00',
-        int(block) << 40 | int(tx) << 16 | int(out),
-        int(n['amount_msat']),
-        blockheight + n['delay'])).decode('ASCII')
-    payload += "00" * 12
-    return payload
-
-
-def buildpath(plugin, node_id, payload, amt, exclusions):
-    blockheight = plugin.rpc.getinfo()['blockheight']
-    route = plugin.rpc.getroute(node_id, amt, 10, exclude=exclusions)['route']
-    first_hop = route[0]
-    # Need to shift the parameters by one hop
-    hops = []
-    for h, n in zip(route[:-1], route[1:]):
-        # We tell the node h about the parameters to use for n (a.k.a. h + 1)
-        hops.append({
-            "type": "legacy",
-            "pubkey": h['id'],
-            "payload": serialize_payload(n, blockheight)
-        })
-
-    pl = TlvPayload()
-    pl.fields.append(Tu64Field(2, amt))
-    pl.fields.append(Tu32Field(4, route[-1]['delay']))
-
-    for f in payload.fields:
-        pl.add_field(f.typenum, f.value)
-
-    # The last hop has a special payload:
-    hops.append({
-        "type": "tlv",
-        "pubkey": route[-1]['id'],
-        "payload": hexlify(pl.to_bytes()).decode('ASCII'),
-    })
-    print(f"Keysend payload {hexlify(pl.to_bytes())}")
-    return first_hop, hops, route
-
-
-def deliver(node_id, payload, amt, payment_hash, max_attempts=5):
-    """Do your best to deliver `payload` to `node_id`.
-    """
-    exclusions = []
-    payment_hash = hexlify(payment_hash).decode('ASCII')
-
-    for attempt in range(max_attempts):
-        plugin.log("Starting attempt {} to deliver message to {}".format(attempt, node_id))
-
-        first_hop, hops, route = buildpath(plugin, node_id, payload, amt, exclusions)
-        onion = plugin.rpc.createonion(hops=hops, assocdata=payment_hash)
-
-        plugin.rpc.sendonion(
-            onion=onion['onion'],
-            first_hop=first_hop,
-            payment_hash=payment_hash,
-            shared_secrets=onion['shared_secrets'],
-        )
-        try:
-            plugin.rpc.waitsendpay(payment_hash=payment_hash)
-            return {'route': route, 'payment_hash': payment_hash, 'attempt': attempt}
-        except RpcError as e:
-            failcode = e.error['data']['failcode']
-            failingidx = e.error['data']['erring_index']
-            if failcode == 16399 or failingidx == len(hops):
-                return {
-                    'route': route,
-                    'payment_hash': payment_hash,
-                    'attempt': attempt + 1
-                }
-
-            plugin.log("Retrying delivery.")
-
-            # TODO Store the failing channel in the exclusions
-    raise ValueError('Could not reach destination {node_id}'.format(node_id=node_id))
-
-
-@plugin.method('keysend')
-def keysend(node_id, amount, plugin):
-    payload = TlvPayload()
-    payment_key = os.urandom(32)
-    payment_hash = hashlib.sha256(payment_key).digest()
-    payload.add_field(TLV_KEYSEND_PREIMAGE, payment_key)
-    res = deliver(
-        node_id,
-        payload,
-        amt=amount,
-        payment_hash=payment_hash
-    )
-    return res
-
-
-plugin.run()